Technical Abstract:
An expert consultation for FAO/WHO subjectively set the Recommended Nutrient Intakes (RNIs) for magnesium at 260 and 220 mg/day for men and women, respectively. The Scientific Committee for Food of the European Communities determined the acceptable range of magnesium intakes to be 150-500 mg/day. The NHANES 2001-2002 estimated that the magnesium intakes of 25% of adult men and women were less than or equal to 251 and 184 mg/day and 10% of adult men and women were less than or equal to 206 and 148 mg/day, respectively, in the U.S. The disconnect between reports that many people do not consume recommended intakes of magnesium, but that it is rare to find functional changes attributed to simple dietary magnesium deficiency in otherwise healthy adults, prompted a series of human magnesium deprivation experiments at the Grand Forks Human Nutrition Research Center. In the experiments described here and approved by the University of North Dakota Institutional Review Board, postmenopausal women resided in a metabolic unit that provided a common environment for strict control of food consumption, weight, exercise, and data collection. The women were fed Western-type diets providing mean magnesium intakes ranging from 100-150 mg (4.1-6.2 mmol)/day and mean calcium intakes ranging from 695-813 mg (17.3-20.3 mmol)/day for 6-13 weeks. Magnesium was replenished by supplements of magnesium gluconate that increased mean intakes from 320-350 mg (13.2-14.4 mmol)/day. A negative magnesium balance was used to establish that magnesium intakes were inadequate and decreased magnesium status was confirmed by decreased erythrocyte or muscle magnesium and highly positive magnesium balance upon magnesium supplementation. Functional changes induced by magnesium deprivation included heart arrhythmias (atrial flutter and fibrillation and increased ventricular premature discharges), and decreased energy efficiency characterized by increased peak oxygen uptake, total and cumulative net oxygen uptake and peak heart rate during a submaximal exercise test. Biochemical changes induced by magnesium deficiency included calcium retention (increased calcium balance) and increased phosphorous and decreased potassium urinary excretion. Changes in calcium and potassium metabolism suggest disturbed cellular ionic balance. The calcium was most likely retained in soft tissue cells because animal experiments have shown that magnesium deficiency increases muscle calcium. Increased intracellular calcium can lead to changes in potassium utilization, heart arrhythmias and increased oxidative stress. Magnesium deprivation increased erythrocyte superoxide dismutase which suggests increased oxidative stress. Under the experimental conditions used, including assuring adequate intakes of all known essential nutrients except magnesium, intakes of 695-813 mg calcium/day did not result in mean negative calcium balances, but they were close to zero when magnesium intakes were adequate. The findings show that plausible low dietary magnesium intakes have functional and biochemical consequences related to cardiovascular health, and suggest that under optimal conditions, calcium intakes between 700-800 mg/day are adequate for post menopausal women.